Niemann-Pick Disease is a progressively debilitating, neurogenetic disorder which is characterized biochemically by the accumulation of sphingomyelin in several tissues and organs in conjunction with deficiency of the lysosomal hydrolase, sphingomyelinase. Several ill-defined phenotypes of Niemann-Pick Disease have been reported in the clinical literature. Detailed description of these various phenotypes in terms of cellular pathochemistry and molecular genetics has not been accomplished to date. A major obstacle in this area has been the consistent absence of reproducible techniques for the isolation of hemogeneous preparations of sphingomyelinase. Employing novel detergent and chromatography systems, we have successfully and reproducibly purified sphingomyelinase to homogeneity. The purified enzyme migrates with an apparent molecular weight of 52,000 daltons in SDS-polyacrylamide gels under both reducing and nonreducing conditions. Detailed kinetic analyses and determinations of the primary protein structure and carbohydrate composition are in progress as are efforts to develop and characterize monoclonal and polyclonal antibodies to the purified enzyme. Availability of well characterized antibodies will allow us to proceed immediately to cloning of the gene for sphingomyelinase. Characterization of the phenotypes of Niemann-Pick Disease in terms of protein polymorphisms and specific mutations at the DNA level will become a reality.